The present invention relates to a golf club and a method of manufacturing the same, and more specifically, it relates to a structure of a golf club head formed by integrally forming a face portion and a neck portion and a method of manufacturing the same.
The head part of a golf club includes a face portion having a stroking surface and a neck portion connecting this face portion with a shaft. While the face portion and the neck portion are integrally formed in a golf club head manufactured by forging in general, the neck portion is so readily deformed in stroking that the neck portion must be thickened and it is difficult to reduce mass distribution to the neck portion. Further, the face portion and the neck portion are formed in different steps respectively and thereafter connected with each other. Therefore, strength on the connected parts of the face portion and the neck portion is disadvantageously reduced.
To this end, the inventors have made deep study on the reason therefor, to recognize that metal flow lines discontinue on the aforementioned connected parts. They have further investigated metal flow lines in various conventional products, to find those shown in FIGS. 20 to 24. In a golf club head shown in these figures, metal flow lines 3 partially continue on connected parts of a face portion 1 and a neck portion 2, and hence it is inferable that strength on the connected parts improves.
Also in this example, however, the metal flow lines 3 are toward various directions on the face portion 1 as shown in FIG. 21, and get inhomogeneous on the face portion 1. Therefore, hardness of the face portion 1 gets so inhomogeneous as shown in FIG. 25 that strength varies with portions of the face and the thickness of the face must be designed in response to a portion inferior in strength and disadvantageously hard to reduce.
The present invention has been proposed in order to solve the aforementioned problem. An object of the present invention is provide a golf club having a wide sweet spot by rendering metal flow lines continuously extend over a neck portion and a face portion and rendering the metal flow lines extend in a single direction on the face portion thereby homogenizing hardness of the face portion while improving strength on the aforementioned connected parts and reducing the thickness of the face or reducing the diameter of the neck for applying residual mass thereof to a portion around the head.
The golf club according to the present invention comprises a face portion having a stroking surface (ball hitting surface) and a neck portion connecting the face portion with a shaft, and metal flow lines (grain flows) continue from the neck portion to the face portion while the metal flow lines extend in a single direction on the face portion.
The metal flow lines thus continue from the neck portion to the face portion, whereby strength on the connected parts of the neck portion and the face portion can be improved. Further, the metal flow lines extend in a single direction on the face portion, whereby hardness of the face portion can be homogenized.
The aforementioned metal flow lines preferably extend in the aforementioned single direction on the stroking surface. Further, the metal flow lines preferably extend along a plane parallel to the stroking surface. In addition, the metal flow lines preferably extend from the neck portion in a direction toward a toe of the face portion.
The difference between the maximum value and the minimum value of Vickers hardness ((Hv) with a load of 2 kg) on a stroking portion of the aforementioned face portion is preferably not more than 30. Vickers hardness on the stroking portion is preferably at least 130 and not more than 160. More preferably, Vickers hardness on the stroking portion is at least 140 and not more than 160. The stroking portion refers to a surface portion of the face portion reaching a prescribed depth from the stroking surface, which is a portion planned to stroke from the first.
The golf club according to the present invention comprises a face portion and a neck portion integrally formed by bending a rod member reduced in sectional area by drawing plastic working and thereafter forging the rod member.
The inventors have recognized that a golf club manufactured by the aforementioned method attains the aforementioned excellent effect.
A method of manufacturing a golf club according to the present invention comprises the following steps: A rod member reduced in sectional area by drawing plastic working is subjected to bending. After this bending, the rod member is subjected to forging for integrally forming a face portion and a neck portion.
Metal flow line density of a portion for defining the neck portion can be improved in the rod member, for example, by performing drawing plastic working in the aforementioned manner. The rod member can be bent while keeping the metal flow lines effective by performing bending on the rod member in this state. The face portion and the neck portion can be integrally formed while keeping the metal flow lines effective to the maximum by forging the bent rod member.
The aforementioned drawing plastic working is preferably performed to plastically work a first end of the rod member to be smaller in sectional area than a second end while increasing metal flow line density on the first end of the rod member. The aforementioned drawing plastic working may be performed by rolling an end of the rod member, for example.
The aforementioned forging step preferably includes a first forging step of performing rough forging on the rod member a plurality of times for approximating the shape of the rod member to a final shape while ensuring metal flow lines and a second forging step of performing precision forging on a material obtained after the rough forging for working the material into the final shape. Thus, forging can be performed while keeping the metal flow lines effective.
The neck portion is formed on a first end of the rod member subjected to drawing plastic working, and the face portion is formed on a second end of the rod member.